Any article made of wood is subject to expansion and contraction resulting from changes in humidity. Wood is a hygroscopic material, which means it will absorb moisture in a wet environment and give off moisture in a dry environment until the wood reaches an equilibrium. Approximately a 1% dimension change takes place with each 3% change in the moisture content of the wood. This applies to hardwood more so than soft wood. So the environment that wood is exposed to has a great deal to do with the amount of moisture in the wood. Air can hold a certain amount of moisture at a given temperature when it is saturated. Relative humidity expresses what the air is actually holding compared to what it would hold if the air were saturated. Temperature is important since warm air can hold more moisture than cold air.
Freshly cut trees have a high moisture content. Wood cut from these trees generally will lose much of the moisture as the wood is being processed. Although wood can be brought to a point of relative stability, this does not mean that the wood will not change. In the summer when the air has relatively high moisture content wood will absorb moisture, whereas in the winter with low moisture contents wood will lose moisture. This loss of moisture is particularly true in centrally heated houses where the moisture contents tends to quite low.
Often these changes in the moisture content of hardwood floors that occur with changes in the moisture content of air will invariably lead to customer complaints. The result of these changes in moisture content can lead to unsightly gaps between the strips of hardwood, or to floors that creak, cup, buckle or shift and/or having cracks and splits in the flooring. When wood is exposed to air, the wood will dry or pick up moisture until it is in equilibrium with humidity and temperature of the air. Moisture absorption causes wood to swell unequally in a variety of directions. When it dries wood shrinks across the grain. This is true of all woods. It is also true that moisture absorption will cause wood to swell unequally, in a variety of directions. Another truth is that all wood will continue to expand or contract with changes in humidity no matter what you do to it (save shrink wrapping it in an air tight plastic wrapper).
Thus, it would be advantageous if there were a means available that would provide hardwood floors that would not be subject to absorption or loss of moisture because of the humidity and temperature variations that occur in the environment in which the wood is placed in.